It has been known to employ a releasable dye as the coupling-off group to provide a so-called `high dye-yield` coupler. Such a coupler reacts with oxidized color developer to form one dye and in doing so releases a second dye. The net result is the formation of two molecules of dye with 2-equivalents of silver. It enables one to reduce the amount of coupler, silver, and other materials to be included in the film layers. It also enables thinner layers which in turn reduce the amount of light scatter to improve sharpness in underlying layers. Thinner layers can also reduce the level of unwanted absorption which can further enhance the image quality in underlying layers. The benefits of the high dye-yield couplers are thus particularly advantageous in the uppermost layers, i.e., in the blue sensitive layers, in conventional color negative layer arrangements.
The first useful high dye-yield couplers have been disclosed by J. Mooberry and S. Singer in U.S. Pat. No. 4,840,884. J. Mooberry, et. al. have later disclosed improved high dye-yield couplers with methine dye chromophore in U.S. Pat. No. 5,457,004. The latter patent teaches a few advantages of using the methine dyes. Compared to couplers releasing analogous azo dyes, the couplers releasing methine dyes provide much higher extinction and superior photographic properties such as hue and dispersibility.
One of the obstacles in commercializing high dye-yield couplers is difficulty of synthesis. The complex molecule requires a number of synthetic steps some of which are too difficult to adapt in a large scale manufacturing. In the J. Mooberry, et al. patent a method has been described for synthesis of a high dye-yield yellow coupler. It requires a large number of synthetic steps and the yield of product is less than desired.
U.S. Pat. No. 5,457,004 discloses the use of alkylaminoarylcarbonyl intermediate compounds. A method for the synthesis of the high dye-yield coupler relies on such an intermediate to begin the preparation of the coupler. It is therefore a problem to be solved to provide a general method of making and using alkylaminoarylcarbonyl compounds which serve as the starting materials or intermediates.